1. Field of the Invention
The present invention relates generally to devices for blast-cleaning surfaces and particularly, but not by way of limitation, to a rotatable blast wheel for propelling abrasive material against a surface to be blast-cleaned.
2. Description of Related Art
Several types of blast wheels have been used in blast-cleaning machines over the years. One type of blast-wheel is disclosed in U. S. Pat. No. 4,377,924 issued to Bergh. This particular device is called a "centrifugal blasting wheel" or a "center feed throwing wheel." Abrasive material is fed to a cage in the center of the wheel, which has a hub and a number of blades extending radially outward from the hub. The cage dispenses abrasive material to the blades, which throw the abrasive material in a direction controlled by the cage.
The Bergh device is subject to wear with respect to the cage, the hub and the blades. Thus, the capability of the Bergh blast wheel to center feed and throw abrasive material is bought at the cost of additional components being subjected to wear and ultimate replacement.
Another type of blast wheel is sometimes called a "paddle wheel", the construction of which is disclosed in U.S. Pat. No. 4,416,092 issued to Nelson. This wheel has a drum and a number of blades extending radially outward from the drum. Abrasive material is fed generally along a tangent to the drum and the blades strike the abrasive material toward the surface to be blast-cleaned as the drum is rotated.
The Nelson blast wheel is simpler in construction than the center feed throwing wheel. However, the striking action of the paddle wheel blades is noisier than the throwing operation of the centrifugal wheel. Further, the drum construction of the Nelson blast wheel augments the noise created by the paddle wheel blades.